Liquid crystal display device

ABSTRACT

It is an object of the invention to provide a liquid crystal display device which permits both miniaturization and cost reduction to be realized and has a high reliability. A device comprises a driving substrate ( 11 ) having wiring layers ( 18   a   , 18   b ), an opposite substrate ( 21 ) having an opposite electrode ( 24 ), a sealing ( 31 ) member disposed between the driving substrate ( 11 ) and the opposite substrate ( 21 ), and a liquid crystal layer ( 41 ) formed by a liquid crystal material sealed by the sealing member ( 31 ) in the space between the driving substrate ( 11 ) and the opposite substrate ( 21 ). A side face ( 11   a ) of the driving substrate ( 11 ) is flush with a side face ( 21   a ) of the opposite substrate ( 21 ). The wiring layers ( 18   a   , 18   b ) extend to an edge of the side face ( 11   a ) of the driving substrate ( 11 ), an end of the wiring layers ( 18   a   , 18   b ) having a possibility to contact with the atmosphere, the opposite electrode ( 24 ) extending to or near to an edge of the side face ( 21   a ) of the opposite substrate ( 21 ). A dielectric member ( 16 ) having a relative dielectric constant equal to or less than 5 is disposed between the wiring layers ( 18   a   , 18   b ) and the opposite electrode ( 24 ) at least on the side of the sealing member ( 31 ) remote from the liquid crystal layer ( 41 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device in which a liquid crystal material is sealed by a sealing member between a first substrate having a first conductive member and a second substrate having a second conductive member, and more particularly, to a narrow-framed liquid crystal display device whose area other than the display area is reduced.

2. Description of Related Art

With electronic devices provided with a liquid crystal display device represented by a cellular phone and personal computer getting rapidly widespread in recent years, there is a strong demand for a liquid crystal display device realizing miniaturization and cost reduction. While there is such a strong demand for miniaturization of the entire device, there is another demand that the area of the display section should be expanded. For this purpose, a process of narrowing the width of the portion peripheral to the display section (frame section), or so-called “frame-narrowing” is underway. The peripheral portion is a space disposed with wiring for supplying power to TFTs (thin film transistors) used for switching of a liquid crystal material and terminals for bonding IC chips making up a driving circuit and this space is conventionally disposed with circuits on all the peripheral portions at the upper edge, lower edge, right edge and left edge. However, with the progress of frame-narrowing, the circuits are recently provided only on the lower peripheral portion. On the other hand, with respect to the demand for cost reduction, there is a demand for a reduction of the number of masks at the manufacturing stage. In response to this demand, patterning of layers made of different materials is realized with a single mask.

FIGS. 1A and 1B show an exemplary structure of a conventional liquid crystal display device when both of the above-described frame-narrowing and reduction of the number of masks are realized. FIG. 1A is a plan view of the device and FIG. 1B is a cross sectional view of the device taken along a line IIIB-IIIB of FIG. 1A. When viewed from the top, this liquid crystal display device 100 is constructed of a display section 101 and a peripheral portion 102 around the display section 101. On the lower peripheral portion 102 a of the peripheral portion 102, there is a circuit 103 provided with a display section driving circuit electrically connected to the display section 101 and a controller for controlling the driving circuit and the remaining three sides remain free, intended to enhance the effect of frame-narrowing.

As shown in FIG. 1B, this liquid crystal display device 100 has a configuration that a liquid crystal material 141 is disposed between a driving substrate 111 and an opposite substrate 121 and the liquid crystal material 141 is sealed by a sealing member 131 provided in a boundary area between the display section 101 and the peripheral portion 102. On the driving substrate 111, a wiring layer 118 a of indium tin oxide (ITO) and a wiring layer 118 b of an alloy of molybdenum (Mo) and chromium (Cr) are formed and these layers extend to an edge of the driving substrate 111. An insulating layer 119 is formed on the wiring layer 118 b and a flattening film 116 is formed inside the sealing member 131 on the insulating layer. The wiring layers 118 a and 118 b are created through patterning by means of a single mask. As the material of the insulating layer 119, for example, silicon nitride (SiNx) is used considering adhesion to the material of the sealing member 131. On the other hand, the opposite substrate 121 is provided with an opposite electrode 124 that extends to or near to an edge of the opposite substrate 121 together with a light shielding film (black matrix) 122 and a color filter 123.

In the liquid crystal display device 100, at the peripheral portion in the above-described free state, that is, the area where no circuit exists, the end (parting plane) 111 a of the driving substrate 111 and the end 121 a of the opposite substrate 121 form a so-called flush-structure. At the lower peripheral portion 102 a provided with the circuit 103 of the peripheral portion 102, the driving substrate 111 is larger than the opposite substrate 121 so that the wiring layers 118 a and 118 b on the driving substrate side do not face the opposite electrode 124 on the opposite substrate side. However, in the area where no circuit exists, the wiring layers 118 a and 118 b are disposed opposite to the opposite electrode 124 even at the edge of the substrate. In this area, the ends of the wiring layers 118 a and 118 b are exposed without being covered with any insulating layer due to the aforementioned mask-saving process and the ends of the wiring layers 118 a and 118 b have direct contact with the atmosphere. When the device is driven in this condition, an electric field is produced between the wiring layers 118 a and 118 b and opposite electrode 124 facing mutually due to a potential difference therebetween, and the portions of the wiring layers 118 a and 118 b that have contact with the atmosphere are subject to a chemical reaction with water, etc., in the atmosphere, which leads to a problem of corrosion of the wiring layers 118 a and 118 b. Thus, efforts to realize miniaturization and cost reduction with the conventional liquid crystal display device end up with a problem that the reliability of the device degrades due to corrosion of the wiring layers and the problem becomes more conspicuous especially when the wiring layers are made of metal.

SUMMARY OF THE INVENTION

The present invention has been implemented in view of the above-described problems and it is an object of the present invention to provide a liquid crystal display device capable of realizing miniaturization and cost reduction as well as providing high reliability, and more specifically, to provide a high reliability liquid crystal display device with corrosion of wiring layers in the peripheral portion suppressed.

The liquid crystal display device according to the present invention comprises a first substrate having a first conductive member, a second substrate disposed opposite to the first substrate with a given space therebetween and having a second conductive member on its surface opposite to the first conductive member of the first substrate, a sealing member disposed between the first substrate and the second substrate and a liquid crystal layer formed by a liquid crystal material sealed by the sealing member in the space between the first substrate and the second substrate, characterized in that a side face of the first substrate and a side face of the second substrate corresponding to the side face of the first substrate are present substantially in the same plane, that the first conductive member extends to an edge of the side face of the first substrate, an end of the first conductive member on a side of the side face of the first substrate having a possibility to contact with the atmosphere, the second conductive member extending to or near to an edge of the side face of the second substrate, and that a dielectric member having a relative dielectric constant equal to or less than 5 is disposed between the first conductive member and the second conductive member at least on the side of the sealing member remote from the liquid crystal layer.

Since the liquid crystal display device according to the present invention is provided with a dielectric member having a relative dielectric constant equal to or less than 5 between the first conductive member and the second conductive member on the side of the sealing member remote from the liquid crystal layer, a potential difference between the first conductive member and second conductive member becomes relatively smaller during driving and the electric field produced therebetween is reduced. For this reason, corrosion of the part of the end of the first conductive member that has contact with the atmosphere is suppresses and the device has high reliability.

Furthermore, for the liquid crystal display device according to the present invention, it is preferable that the dielectric member extends to the edge of the side face of the first substrate. This suppresses corrosion of the first conductive member more effectively, and can thereby further improve the reliability of the device.

Furthermore, for the liquid crystal display device according to the present invention, it is preferable that the first substrate is further provided with depressions or projections which are spaced apart from each other on the same side as that on which the first conductive member is provided, and a reflecting film which is rendered uneven under the influence of the depressions or projections and has a function of reflecting a light and that the dielectric member is provided so as to extend from the side of the sealing member remote from the liquid crystal layer to the side of the liquid crystal layer as an integral member, the dielectric member being disposed between the depressions or projections and the reflecting film on the liquid crystal layer's side of the sealing member. In the case of such a reflective type liquid crystal display device, providing the dielectric member from the side of the sealing member remote from the liquid crystal layer to the side of the liquid crystal layer as an integral member allows a single layer to have each functions of the sealing member on the liquid crystal layer's side and the remote side of the sealing member. This simplifies the configuration of the device. In this case, it is preferable that the dielectric member is in contact with the sealing member and that the dielectric member is made of a resin and the sealing member is made of a thermosetting resin because this will enhance adhesion therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a conventional exemplary liquid crystal display device, and FIG. 1B is a cross sectional view of the device taken along a line IIIB-IIIB of FIG. 1A.

FIG. 2 is a cross sectional view of a liquid crystal display device according to an embodiment of the invention;

FIG. 3 is another cross sectional view of the liquid crystal display device according to the embodiment of the invention;

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

With reference now to the accompanying drawings, an embodiment of the present invention will be described in detail below.

First, a configuration of a liquid crystal display device according to an embodiment of the present invention will be explained. FIGS. 2 and 3 show the liquid crystal display device according to this embodiment. When viewed from the top, the liquid crystal display device according to this embodiment is constructed of a display section and a peripheral portion peripheral to the display section as in the case of above-described FIG. 1A and is provided with a circuit on one side of the peripheral portion. FIG. 2 is a cross sectional view of the area of the peripheral portion where no circuit exists and its periphery, and FIG. 3 is a cross sectional view of the display section.

This liquid crystal display device is provided with a driving substrate 11 as a first substrate and an opposite substrate 21 as a second substrate disposed opposite to the driving substrate 11 with a given space therebetween and a sealing member 31 is disposed between the driving substrate 11 and the opposite substrate 21. A liquid crystal layer 41 is formed by a liquid crystal material sealed by the sealing member 31 in the space between the driving substrate 11 and the opposite substrate 21. The driving substrate 11 and the opposite substrate 21 form a so-called “flush-structure” in the area of the peripheral portion without any circuit (FIG. 2) in which their respective side faces 11 a and 21 a are present substantially in the same plane.

In the display section, as shown in FIG. 3, the driving substrate 11 is provided, on its surface facing the opposite substrate, with source electrodes 12 a electrically connected to respective data lines and drain electrodes 12 b, with a space being disposed therebetween, and a semiconductor layer 12 c is formed adjacent to the source electrodes 12 a and the drain electrodes 12 b. Gate electrodes 14 electrically connected to respective scanning lines (not shown) are formed on the side of the semiconductor layer 12 c remote from the driving substrate 11, with a gate insulating film 13 having an opening being formed between the semiconductor layer 12 c and the gate electrodes 14. Thus, TFTs are provided on the side of the driving substrate 11 facing the opposite substrate 21. The TFTs are placed in a form of, for example, a matrix in a one-to-one correspondence with pixel electrodes, which will be described later. A pattern of depressions or projections 15 provided with a space therebetween is formed on the gate insulating film 13 and the gate electrode 14 and a flattening film 16 is provided, as a dielectric material, on the pattern of depressions or projections 15 with an opening. A reflecting film (reflecting electrode) 17 also functioning as a pixel electrode is formed on the flattening film 16. The reflecting film 17 is electrically connected, for example, with the drain electrodes 12 b through the openings provided in the flattening film 16 and the gate insulating film 13 and voltages are applied thereto using the above-described TFTs. The driving substrate 11 is further provided with an orientation film (not shown), and so on.

Furthermore, in the area or in the vicinity of the peripheral portion of this liquid crystal display device where no circuit exists, the wiring layers 18 a and 18 b are formed as the first conductive members on the side of the driving substrate 11 opposite to the opposite substrate 21 as shown in FIG. 2. These wiring layers 18 a and 18 b extend to an edge constituting the side face 11 a of the driving substrate 11, which has a possibility to contact with the atmosphere. The wiring layer 18 a is made, for example, of ITO and used as a terminal of the display section. The wiring layer 18 b is made, for example, of an alloy of molybdenum and chromium, forming a data line. On the wiring layers 18 a and 18 b, the flattening film 16 extends, for example, to the edge constituting the side face 11 a of the driving substrate 11, with the insulating film 19 being formed between the wiring layer 18 b and the flattening film 16.

The above-described components on the driving substrate 11 are created in such a way that, for example, the source electrodes 12 a, the drain electrodes 12 b and the wiring layers 18 a and 18 b are patterned, the semiconductor layer 12 c is patterned, the gate insulating film 13 is patterned, and then the gate electrodes 14, depressions or projections 15, the flattening film 16 and the reflecting electrode 17 are patterned one by one.

On the other hand, a light shielding film 22, a color filter 23, the opposite electrode 24 as the second conductive member and an orientation film (not shown), etc., are formed on the surface of the opposite substrate 21 facing the driving substrate side. The opposite electrode 24 extends to or near to the edge of the side face 21 a of the opposite substrate 21 (near the edge in FIG. 2). Though not shown here, a polarizing plate, etc., is formed on the side of the opposite substrate 21 remote from the driving substrate 11.

Secondly, the flattening film 16, which constitutes a characteristic portion of the liquid crystal display device according to this embodiment, will be explained in more detail below.

The flattening film 16 is made of a dielectric member having a relative dielectric constant equal to or less than 5, or more preferably equal to or less than 3.5, for example, 2 to 3.5, and more specifically made of, for example, a resin. This flattening film 16 is intended to adjust unevenness of the reflecting film 17 rendered uneven by the patterned depressions or projections 15 (refer to Japanese Patent Application No.2001-308737). In this embodiment, the flattening film 16 made of the above-described dielectric member is disposed up to an edge of the driving substrate 11 and inserted between the wiring layers 18 a and 18 b and the opposite electrode 24, each extending to the edge of the substrate, and therefore a potential difference between the wiring layers 18 a and 18 b and opposite electrode 24 during driving is relatively small and the intensity of the electric field therebetween is also small. Considering the function as the dielectric in such a peripheral portion of the apparatus, the smaller the relative dielectric constant of the dielectric member constituting the flattening film 16, the more preferable. The reason that the relative dielectric constant is set to be equal to or less than 5 is that with a relative dielectric constant exceeding 5, it would be impossible to obtain a sufficient effect unless the film thickness is increased considerably. The thickness of the flattening film 16 is, for example, 1 μm to 5 μm.

In this embodiment, the sealing member is provided on and in contact with the flattening film 16 and the level of adhesion between the flattening film 16 and the sealing member 31 is required to be high. For this reason, when the resin is used as the material of the flattening film 16, it is preferable to use a thermosetting resin for the sealing member 31.

The liquid crystal display device with the above-described configuration will operate as follows.

In this liquid crystal display device, a scanning voltage is sequentially supplied from the circuit to the gate lines through the wiring layer 18 a cyclically and signal voltages are selectively supplied to the respective wiring layers 18 b (data lines) in accordance with image signals. A given voltage is constantly supplied to the opposite electrode 24. The signal voltages are supplied to the reflecting electrodes (pixel electrodes) 17 through TFTs which have turned on with a scanning voltage supplied sequentially, which provides a voltage to the liquid crystal layer 41 between the opposite electrode 24 and the reflecting electrode 17 and allows a desired image display to be performed.

In this case, since the flattening film 16 made of a dielectric member having a relative dielectric constant equal to or less than 5 is formed between the wiring layers 18 a and 18 b and the opposite electrode 24 in the area of the peripheral portion where no circuit exists, the potential difference between the wiring layers 18 a and 18 b and the opposite electrode 24 becomes relatively smaller and the electric field produced therebetween is reduced. This suppresses corrosion of the areas of the wiring layers 18 a and 18 b in contact with the atmosphere.

As described above, the liquid crystal display device according to this embodiment is provided with the flattening film 16 made of a dielectric member having a relative dielectric constant equal to or less than 5 between the wiring layers 18 a and 18 b and the opposite electrode 24, and can thereby reduce the potential difference between the mutually facing wiring layers 18 a and 18 b and opposite electrode 24 in the area of the peripheral portion where no circuit exists when a voltage is applied to the wiring layers 18 a and 18 b and the opposite electrode 24 and reduce the electric field produced therebetween due to this potential difference. Therefore, even when the ends of the wiring layers 18 a and 18 b contact with the atmosphere, a reaction between the wiring layers 18 a and 18 b and water, etc., in the atmosphere is suppressed so that the corrosion rate of the wiring layers 18 a and 18 b can be reduced considerably. Thus, this embodiment can implement a small, highly reliable liquid crystal display device in fewer patterning steps and make the device highly reliable even in a high temperature, high humidity operating environment in particular.

Furthermore, with the above-mentioned liquid crystal display device, since the flattening film for adjusting unevenness on the surface of the reflecting film 17 is further extended to insert the dielectric member between the wiring layers 18 a and 18 b and the opposite electrode 24, it is possible to suppress corrosion of the wiring layers 18 a and 18 b with a simple structure without providing any additional film, realizing cost reduction in this respect, too.

Furthermore, composing the flattening film 16 of a resin and composing the sealing member 17 of a thermosetting resin can enhance adhesion between the flattening film 16 and the sealing member 17 and thereby implement a high reliability liquid crystal display device.

The present invention has been explained with reference to the embodiment, but the present invention is not limited to the above-described embodiment and can be modified in various ways. For example, the above-described embodiment has described the case where the flattening film necessary inside the display section is extended to an edge of the driving substrate, but it is also possible to insert a dielectric member, in the peripheral portion, between the wiring layers 18 a and 18 b and the opposite electrode 24 aside from the flattening film 16. Moreover, the above-described dielectric member need not necessarily be extended to an edge of the substrate, but the effect of the present invention can be obtained when the dielectric member is provided into, in the peripheral portion, at least a part between the wiring layers 18 a and 18 b and the opposite electrode 24.

Furthermore, the above-described embodiment has described an example of the first conductive member having a multilayer structure consisting of the wiring layers 18 a and 18 b, but the first conductive member can also have a single-layer structure. The second conductive member may have a multilayer structure.

Furthermore, the above-described embodiment has described an example of a patterning method on the driving substrate, but the present invention is also effective for a device manufactured using any method other the above-described patterning method if the device has a structure that the end faces of the wiring layers 18 a and 18 b contact with the atmosphere.

Furthermore, the above-described embodiment has described the liquid crystal display device provided with so-called top gate type TFTs, but the device can also be adapted so as to have so-called bottom gate type TFTs. Furthermore, the above-described embodiment has described the liquid crystal display device with an active matrix display using TFTs as switching elements, but the device can also be adapted so as to have other switching elements such as MOSFET (metal oxide semiconductor field effect transistor). Moreover, the present invention is also applicable to a passive matrix display device without using any switching element.

Furthermore, the above-described embodiment has described the reflective type liquid crystal display device, but the present invention is also applicable to a liquid crystal display device having a combined structure of a reflective type and transmission type or a liquid crystal display device with the reflecting film 17 whose thickness is reduced so as to reflect part of light and allow part of light to penetrate. In addition, the present invention is also applicable to a transmission type liquid crystal display device, in which case a flattening film provided on the driving substrate to increase an open area ratio can also be used in the same way as the above-described flattening film 16. 

1. A liquid crystal display device comprising: a first substrate having a first conductive member; a second substrate disposed opposite to the first substrate with a given space therebetween and having a second conductive member on its surface opposite to the first conductive member of the first substrate; a sealing member disposed between the first substrate and the second substrate; and a liquid crystal layer formed by a liquid crystal material sealed by the sealing member in the space between the first substrate and the second substrate, said liquid crystal display device characterized: in that a side face of the first substrate and a side face of the second substrate corresponding to said side face of the first substrate are present substantially in the same plane; in that the first conductive member extends to an edge of said side face of the first substrate, an end of the first conductive member on a side of said side face of the first substrate having a possibility to contact with the atmosphere, the second conductive member extending to or near to an edge of said side face of the second substrate; and in that a dielectric member having a relative dielectric constant equal to or less than 5 is disposed between the first conductive member and the second conductive member at least on the side of the sealing member remote from the liquid crystal layer.
 2. A liquid crystal display device as claimed in claim 1, characterized in that the dielectric member extends to the edge of the side face of the first substrate.
 3. A liquid crystal display device as claimed in claim 1, characterized: in that the first substrate is further provided with depressions or projections which are spaced apart from each other on the same side as that on which the first conductive member is provided, and a reflective film which is rendered uneven under the influence of the depressions or projections and has a function of reflecting a light; and in that the dielectric member is provided so as to extend from the side of the sealing member remote from the liquid crystal layer to the side of the liquid crystal layer as an integral member, the dielectric member being disposed between the depressions or projections and the reflective film on the liquid crystal layer's side of the sealing member.
 4. A liquid crystal display device as claimed in claim 3, characterized in that the dielectric member is in contact with the sealing member.
 5. A liquid crystal display device as claimed in claim 4, characterized in that the dielectric member is made of a resin and the sealing member is made of a thermosetting resin. 